#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>

GLboolean doubleBuffer = GL_TRUE;

void draw_background()
{
    //big blue square
    glColor3ub(0,255,255);
    glBegin(GL_QUADS);
    glVertex3i(5, 5, 0);
    glVertex3i(-5, 5, 0);
    glVertex3i(-5, -5, 0);
    glVertex3i(5, -5, 0);
    glEnd();
}
void draw_trangle()
{
    /* transparent triangle */
    glColor3ub(255, 0, 0);
    glBegin(GL_TRIANGLES);
    glVertex3i(-4, -4, 0);
    glVertex3i(4, -4, 0);
    glVertex3i(0, 4, 0);
    glEnd();
}
void draw_blue_square()
{
    /* blue square */
    glColor3ub(0, 0, 200);
    glBegin(GL_QUADS);
    glVertex3i(3, 3, 0);
    glVertex3i(-3, 3, 0);
    glVertex3i(-3, -3, 0);
    glVertex3i(3, -3, 0);
    glEnd();
}

/* ARGSUSED1 */
static void
Key(unsigned char key, int x, int y)
{
    switch (key) {
        case 27:
            exit(0);
    }
}

static void
Draw(void)
{
    int win_width, win_height;
    win_width = glutGet(GLUT_WINDOW_WIDTH);
    win_height = glutGet(GLUT_WINDOW_HEIGHT);

    glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    glViewport(0, 0, win_width, win_height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-10, 10, -10, 10, -1, 1);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glDisable(GL_STENCIL_TEST);
    glStencilMask(0x0);

    draw_background();

    glEnable(GL_STENCIL_TEST);
    glStencilMask(0x1);
    glStencilFunc(GL_ALWAYS, 0x1, 0x1);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    glDepthMask(GL_FALSE);

    draw_trangle();

    glStencilMask(0x1);
    glStencilFunc(GL_NOTEQUAL, 0x1, 0x1);
    glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    glDepthMask(GL_TRUE);

    draw_blue_square();

    if (doubleBuffer) {
        glutSwapBuffers();
    } else {
        glFlush();
    }
}

static void
Args(int argc, char **argv)
{
    GLint i;

    doubleBuffer = GL_TRUE;
    for (i = 1; i < argc; i++) {
        if (strcmp(argv[i], "-sb") == 0) {
            doubleBuffer = GL_FALSE;
        } else if (strcmp(argv[i], "-db") == 0) {
            doubleBuffer = GL_TRUE;
        }
    }
}

int
main(int argc, char **argv)
{
    GLenum type;

    glutInit(&argc, argv);
    Args(argc, argv);

    type = GLUT_RGB | GLUT_STENCIL;
    type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
    glutInitDisplayMode(type);
    glutCreateWindow("Stencil Test");

    glClearColor(0.0, 0.0, 0.0, 0.0);

    glutKeyboardFunc(Key);
    glutDisplayFunc(Draw);
    glutMainLoop();
    return 0;
}